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.TH PCAP_SET_PROTOCOL_LINUX 3PCAP "22 August 2018"
.SH NAME
pcap_set_protocol_linux \- set capture protocol for a not-yet-activated
capture handle
.SH SYNOPSIS
.nf
.ft B
#include <pcap/pcap.h>
.LP
.ft B
int pcap_set_protocol_linux(pcap_t *p, int protocol);
.ft
.fi
.SH DESCRIPTION
On network interface devices on Linux,
.BR pcap_set_protocol_linux ()
sets the protocol to be used in the
.BR socket (2)
call to create a capture socket when the handle is activated.  The
argument is a link-layer protocol value, such as the values in the
.B <linux/if_ether.h>
header file, specified in host byte order.
If
.I protocol
is non-zero, packets of that protocol will be captured when the
handle is activated, otherwise, all packets will be captured.  This
function is only provided on Linux, and, if it is used on any device
other than a network interface, it will have no effect.
.LP
It should not be used in portable code; instead, a filter should be
specified with
.BR pcap_setfilter (3PCAP).
.LP
If a given network interface provides a standard link-layer header, with
a standard packet type, but provides some packet types with a different
socket-layer protocol type from the one in the link-layer header, that
packet type cannot be filtered with a filter specified with
.BR pcap_setfilter ()
but can be filtered by specifying the socket-layer protocol type using
.BR pcap_set_protocol_linux ().
.SH RETURN VALUE
.BR pcap_set_protocol_linux ()
returns 0 on success or
.B PCAP_ERROR_ACTIVATED
if called on a capture handle that has been activated.
.SH BACKWARD COMPATIBILITY
This function became available in libpcap release 1.9.0.
.SH SEE ALSO
.BR pcap (3PCAP),
.BR pcap_create (3PCAP),
.BR pcap_activate (3PCAP)
